FIGS. 1 and 2 show a conventional fuel injector 2. The injector 2 comprises a pilot injector 4 and a pilot swirler 6 for swirling air past the pilot injector 4. A main injector 8 is concentrically positioned around the pilot injector 4 and the pilot swirler 6. An inner main swirler 10 and an outer main swirler 12 are disposed on concentrically inner and outer sides of the main injector 8.
An inner annular member 14 is located between the pilot swirler 6 and the inner main swirler 10. Similarly, an outer annular member 16 is located between the inner main swirler 10 and the outer main swirler 12.
The main injector 8 comprises a plurality of discrete fuel sources (not shown) which are spaced around the circumference of an outer surface of the inner annular member 14. As indicated by the dashed lines, the fuel sources direct jets of fuel towards an inner surface of the outer annular member 16, which forms a prefilmer 18. Alternatively, the fuel may be placed on the prefilmer 18 using a series of discrete slots located around the circumference of the prefilmer 18.
The fuel flows over the surface of the prefilmer 18 prior to being shed from a downstream edge 20 into the swirling airflows. This allows effective atomisation of the fuel.
In an alternative arrangement, the fuel may be supplied to the prefilmer using an annular gallery. Such a gallery supplies a circumferential (i.e. non-discrete) film of fuel onto the prefilmer, and thus creates a uniform circumferential distribution of fuel.
In certain applications, it is desirable to use an injector comprising discrete fuel sources as described above. In order to obtain a circumferential distribution comparable to that provided by an annular gallery, it is desirable to use a larger number of discrete jets. However, there is a limit on the minimum jet hole size in order to prevent blockage from debris and fuel cracking (oxidative coking). Consequently, this limits the number of jets which can fit around the circumference of the injector and also limits the uniformity of the circumferential distribution of the fuel film on the prefilmer.
Accordingly, the present invention seeks to provide a discrete fuel source-type injector which has a more uniform circumferential fuel distribution.